The present invention generally relates to video and audio signal recording and/or reproducing apparatuses, and more particularly to a recording and/or reproducing apparatus for recording and/or reproducing on and/or from a magnetic tape which is transported a frequency modulated audio signal together with a frequency division multiplexed signal comprising a frequency modulated luminance signal and a frequency converted carrier chrominance signal which has been frequency-converted into a low frequency range, by use of rotary magnetic heads mounted at mutually opposing positions on a rotary body to which the magnetic tape is wrapped obliquely for a predetermined angular range.
Presently, in a helical scan type magnetic recording and/or reproducing apparatus (hereinafter simply referred to as a video tape recorder or VTR) for home use employing a magnetic tape having a width of 1/2 inch, the so-called low band conversion color recording and reproducing system is employed because the recording and reproducing frequency band is relatively narrow. According to this low band conversion color recording and reproducing system, a luminance signal separated from a color video signal is frequency-modulated, and a carrier chrominance signal separated from the color video signal is frequency-converted into a frequency band lower than a frequency band of the frequency modulated luminance signal. The frequency modulated luminance signal and the frequency converted carrier chrominance signal are frequency-division-multiplexed to obtain a frequency division multiplexed signal, and this frequency division multiplexed signal is recorded on and reproduced from the magnetic tape. In order to improve the tape utilization efficiency, rotary magnetic heads which record two mutually adjacent tracks have gaps of mutually different azimuth angles so that the tracks can be formed without a guard band therebetween. Furthermore, in order to record and reproduce audio signals with a high quality, there is a conventional VTR which records and reproduces a frequency modulated (FM) audio signal or a pulse code modulated (PCM) audio signal.
However, although the FM audio signal can be transmitted within a narrow frequency band, the phases of reproduced FM audio signals from the rotary heads at a joint portion where the switching of the rotary heads takes place do not coincide perfectly due to differences in the tape tension and the like. As a result, there are problems in that the phase of the reproduced FM audio signal changes at the joint portion and pulse noise corresponding to the change in the phase is generated in a demodulated signal which is obtained by demodulating the reproduced FM audio signal. For this reason, it is necessary to provide a noise reduction circuit for reducing the pulse noise. In addition, since the FM audio signal is an analog signal, the quality of the signal becomes greatly deteriorated when a dub-recording is carried out.
On the other hand, in the case of the PCM audio signal, horizontal and vertical blanking periods are provided and the undesirable effects of the switching of the rotary heads are avoided. Furthermore, in the case of a stereo audio signal, right and left channel audio signals are respectively pulse code modulated and subjected to a time base compression, and PCM audio signals of the right and left channels are recorded time divisionally. Hence, it is possible to avoid transmission during the switching of the rotary heads, and the change in the phase during the switching of the rotary heads can be neglected. Moreover, because the PCM audio signal is a digital signal, the deterioration in the quality of the signal is extremely small when the dub-recording is carried out. Accordingly, in order to record and reproduce the audio signals with a high quality, it is desirable to record the audio signals in the signal format of the PCM audio signal.
However, the frequency spectrum becomes wide when the PCM audio signal is recorded directly on a recording medium, but the error rate becomes high when the frequency band of the PCM audio signal is limited to a predetermined frequency band and it is disadvantageous to transmit within a narrow frequency band. On the other hand, as known systems for transmitting the PCM audio signal having a narrow frequency band, there are the quaternary phase shift keying (QPSK) and the quaternary differential phase shift keying (QDPSK). These known systems enable transmission within a narrow frequency band, but require demodulation of the carrier in a reproducing system. Thus, in the case of the reproduced signal from the VTR including a time base deviation component (jitter), there is a problem in that the circuit construction of the reproducing system becomes complex.